This invention relates to a motor starting switch for use with an electric motor.
Typically, capacitor start and split phase induction motors have a run winding and a starting winding placed in winding receiving slots provided in the bore of a stator core. The starting winding is energized during start up of the motor (or when the speed of the motor falls below a specified operating speed) so as to create a rotating field in the stator and to apply torque on the rotor for starting the motor. However, once the motor has accelerated to a desired operating speed, (e.g., this speed may be 70 percent or more of the normal operating speed of the motor), the rotor is able to follow the alterations of the magnetic field created by the run windings, and the starting winding no longer is needed. Typically, the starting winding is not intended for continuous use and may fail if not deenergized during normal operation of the motor. As is conventional, a switch, referred to as a motor starting switch, is provided in the motor for energizing the starting winding during start up of the motor and for deenergizing the starting winding once the motor has attained its desired operating speed. These motor starting switches are conventionally actuated by a centrifugal actuator mounted on and rotatable with the rotor shaft of the motor. Centrifugal actuators typically include an actuator member movable axially on the rotor shaft from an off or stop position when the motor is stopped (or operating below a specified operating speed) to a run position upon the motor accelerating to a predetermined operating speed. An actuator linkage operatively interconnects the motor starting switch and the actuator member of the centrifugal actuator. As shown in the co-assigned U.S. Pat. No. 4,034,173, this linkage may include a lever interconnecting the switch and actuator member, a spring, and means for adjusting the lever with respect to the actuator. In some instances, the lever is pivoted on a portion of the motor itself, for example on the end shield of the motor. These parts must of necessity be installed before the motor starting switch has been installed in the motor during manufacture thereof.
Because the actuator member of the centrifugal actuator moves only a limited distance between its off and run positions, it has heretofore been necessary to accurately adjust the relative positions of the motor starting switch and the centrifugal actuator so as to ensure that the former is properly actuated by the centrifugal actuator at a specified motor operating speed. This adjustment of the centrifugal actuator with respect to the motor starting switch is a time consuming operation and thus results at least in part for higher labor costs in manufacture of the motor. To ensure that the motor starting switch of certain motor designs is accurately located with respect to the centrifugal actuator, it has been heretofore necessary to accurately cast a mounting surface for the switch or a linkage pivot point on the end shield of the motor. Of course, the requirement of providing a critical switch mounting surface and the lever pivot point on the end shield adds to the expense of die casting the end shields. In other instances, special brackets rigidly secured to the motor have been provided for mounting of the motor starting switch.
Typically, a centrifugal actuator only exerts a relatively light force on the linkage interconnecting the actuator member and the motor starting switch. With prior linkage arrangements, the force exerted on the linkage was, in some instances, too low the actuate the motor starting switch so as to energize the starting winding of the motor upon subsequent start up of the motor. This condition is sometimes referred to as a "stuck" actuator condition and it prevents the motor from starting.
During the service life of a motor, end play (i.e., axial movement) of the rotor shaft with respect to the end shields (or the frame) of the motor may develop. This end play may be sufficient so as to appreciably change the relative position of the centrifugal actuator mounted on the rotor shaft and the motor starting switch rigidly mounted on the frame or end shield of the motor thus affecting operation of the motor starting switch. Under certain end play conditions, the centrifugal actuator could fail to deenergize the starting winding upon the motor attaining its desired operating speed thus causing the starting winding to fail. Under other end play conditions, the centrifugal actuator may fail to reset the motor starting switch to energize the starting winding upon subsequent start up of the motor and thus the motor would fail to start.